Epoxy resin composition, prepreg, and fiber reinforced composite material

ABSTRACT

An object of the present invention is to provide an epoxy resin composition that can be preferably used for prepreg and fiber reinforced composite material applications and is excellent in elastic modulus, strength, and pot life. The present invention is the epoxy resin composition including the following components [A] to [C] and satisfying the following conditions (1) to (4): 
     [A]: epoxy resin
 
[B]: aromatic diamine
 
[C]: a compound having a boiling point of 130° C. or more and a molecular weight m of 50 or more and 250 or less, the compound having no epoxy group in the molecule and having substantially no curing ability of an epoxy resin
         (1): the ratio H/E between the amount by mole, E, of the epoxy group in the component [A] and the amount by mole, H, of active hydrogen in the component [B] is 0.50 or more and 1.30 or less.   (2): at least a part of the component [C] satisfies 0.10 or more and 0.60 or less in a ratio m/M of a molecular weight m thereof to a theoretical molecular weight between crosslinking points, M, of a cured product of the epoxy resin composition.   (3): the ratio C/E of the amount by mole, E, for epoxy groups of the component [A] to the amount by mole, C, of the component [C] satisfying the condition (2) is 0.01 or more and 0.20 or less; and   (4): the viscosity at 70° C. for 2 hours is 5.0 times or less the initial viscosity at 70° C.

TECHNICAL FIELD

The present invention relates to an epoxy resin composition preferablyused for fiber reinforced composite materials for aerospaceapplications, general industrial applications, and sports applications,and a prepreg and a fiber reinforced composite material using the epoxyresin composition.

BACKGROUND ART

Fiber reinforced composite materials in which carbon fibers, aramidfibers and the like are used as reinforcing fibers are widely utilizedin structural materials such as aircraft and motor vehicles, sportsapplications such as tennis rackets, golf shafts, fishing rods,bicycles, and housings, and general industrial applications, due to thehigh specific strength and specific elastic modulus thereof. As theresin composition to be used for this fiber reinforced compositematerial, a thermosetting resin is mainly used from the viewpoint ofheat resistance and productivity, and of these, an epoxy resin ispreferably used from the viewpoint of mechanical properties such asadhesive property with a reinforcing fiber.

In recent years, in order to apply a fiber reinforced composite materialto applications requiring further weight reduction, it is necessary toimprove various physical properties. Therefore, for the purpose ofimproving various mechanical properties of the fiber reinforcedcomposite material, improvement of the elastic modulus, elongation, andstrength of the epoxy resin used as the matrix resin is required.However, an epoxy resin cured product having a high elastic modulus isgenerally brittle, and tends to have low elongation and strength.Therefore, it is a technical problem to simultaneously improve highelastic modulus, elongation, and strength.

In order to improve this problem, various investigations have beenperformed. For example, there has been investigated a method forimproving the elastic modulus and strength by combining an epoxy resinhaving a specific structure and a nanofiller (Patent Document 1). Inaddition, there has been investigated a method for improving the resinstrength by compounding an additive in order to prevent thedicyandiamide used as a curing agent from remaining dissolved andbecoming a defect (Patent Document 2). In addition, there has beeninvestigated a method for using a liquid curing agent that hardly causesdefects in a resin composition for an RTM molding method (PatentDocument 3).

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Laid-open Publication No. 2018-95675

Patent Document 2: WO 2019-181402

Patent Document 3: Japanese Patent Laid-open Publication No. 2014-227473

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

When the technique of Patent Document 1 is used, the mechanicalproperties of the resulting cured resin or fiber reinforced compositematerial are insufficient, and further improvement of the mechanicalproperties is required. In addition, when the technique of PatentDocument 2 is used, the effect of improving the resin strength can beobtained; however, the improvement of the elastic modulus is notconsidered at all, and a technique capable of improving both the elasticmodulus and the strength is required. In addition, when the technique ofPatent Document 3 is used, the resin composition has high reactivity anddoes not have a sufficient pot life for use in prepreg applications.

Therefore, an object of the present invention is to provide an epoxyresin composition that can be preferably used for prepreg and fiberreinforced composite material applications and is excellent in elasticmodulus, strength, and pot life.

Solutions to the Problems

The present invention adopts the following means in order to solve theproblems. That is, the epoxy resin composition includes the followingcomponents [A] to [C] and satisfies the following conditions (1) to (4):

[A]: epoxy resin[B]: aromatic diamine[C]: a compound having a boiling point of 130° C. or more and amolecular weight m of 50 or more and 250 or less, the compound having noepoxy group in the molecule and having substantially no curing abilityof an epoxy resin

(1): the ratio H/E between the amount by mole, E, of the epoxy group inthe component [A] and the amount by mole, H, of active hydrogen in thecomponent [B] is 0.50 or more and 1.30 or less.

(2): at least a part of the component [C] satisfies 0.10 or more and0.60 or less in a ratio m/M of a molecular weight m thereof to atheoretical molecular weight between crosslinking points, M, of a curedproduct of the epoxy resin composition.

(3): the ratio C/E of the amount by mole, E, for epoxy groups of thecomponent [A] to the amount by mole, C, of the component [C] satisfyingthe condition (2) is 0.01 or more and 0.20 or less; and

(4): the viscosity at 70° C. for 2 hours is 5.0 times or less theinitial viscosity at 70° C.

In addition, the present invention provides a prepreg including theepoxy resin composition of the present invention and a reinforcingfiber.

In addition, the present invention provides a fiber reinforced compositematerial including a cured product of the epoxy resin composition of thepresent invention and a reinforcing fiber.

Effects of the Invention

The present invention can provide an epoxy resin composition excellentin elastic modulus, strength, and pot life, the epoxy resin compositioncapable of being preferably used for prepreg and fiber reinforcedcomposite material applications.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the relationship between the ratio C/E of theamount by mole, C, of the component [C] to the amount by mole, E, ofepoxy groups of the component [A], and the elastic modulus, in Example 2(C/E=0.10), Example 5 (C/E=0.02), Example 6 (C/E=0.05), Example 7(C/E=0.16), Comparative Example 1 (C/E=0.00), and Comparative Example 8(C/E=0.23).

FIG. 2 is a graph showing the relationship between the ratio C/E of theamount by mole, C, of the component [C] to the amount by mole, E, ofepoxy groups of the component [A], and the strength, in Example 2(C/E=0.10), Example 5 (C/E=0.02), Example 6 (C/E=0.05), Example 7(C/E=0.16), Comparative Example 1 (C/E=0.00), and Comparative Example 8(C/E=0.23).

FIG. 3 is a graph showing the relationship between the ratio m/M of themolecular weight m of the component [C] to the theoretical molecularweight between crosslinking points, M, of a cured product of an epoxyresin composition and the elastic modulus in Example 1 (m/M=0.29),Example 2 (m/M=0.35), Example 3 (m/M=0.55), Example 4 (m/M=0.40),Comparative Example 1, Comparative Example 4 (m/M=1.40), and ComparativeExample 9 (m/M=0.68). In Comparative Example 1 in which the component[C] was not included, the plot is made at the position of m/M=0.00.

FIG. 4 is a graph showing the relationship between the ratio m/M of themolecular weight m of the component [C] to the theoretical molecularweight between crosslinking points, M, of a cured product of an epoxyresin composition and the strength in Example 1 (m/M=0.29), Example 2(m/M=0.35), Example 3 (m/M=0.55), Example 4 (m/M=0.40), ComparativeExample 1, Comparative Example 4 (m/M=1.40), and Comparative Example 9(m/M=0.68). In Comparative Example 1 in which the component [C] was notincluded, the plot is made at the position of m/M=0.00.

EMBODIMENTS OF THE INVENTION

Hereinafter, the present invention will be described in detail. In thepresent invention, “or more” means the same as or more than thenumerical value indicated therein. In addition, “or less” means the sameas or less than the numerical value indicated therein.

The resin composition of the present invention includes the components[A] to [C] as essential components. In the present invention, the“component” means a compound included in the composition.

The component [A] in the present invention is an epoxy resin. The epoxyresin of the component [A] is preferably an epoxy resin including two ormore epoxy groups in one molecule, because of allowing increasing theglass transition temperature of a cured product obtained by thermallycuring the resin composition and improving the heat resistance. Inaddition, an epoxy resin including one epoxy group in one molecule maybe compounded. These epoxy resins may be used singly or may beappropriately used in combination.

Examples of the epoxy resin of the component [A] include epoxy resinssuch as diaminodiphenylmethane type, diaminodiphenylsulfone type,aminophenol type, bisphenol type, metaxylenediamine type,1,3-bisaminomethylcyclohexane type, isocyanurate type, hydantoin type,phenol novolac type, orthocresol novolac type, trishydroxyphenylmethanetype, and tetraphenylolethane type. Of these, epoxy resins such asdiaminodiphenylmethane type, aminophenol type, and bisphenol type areparticularly preferably used, because of having a good balance ofphysical properties.

Examples of commercially available products of thediaminodiphenylmethane epoxy resin include ELM434 (manufactured bySumitomo Chemical Co., Ltd.), “Araldite (registered trademark)” MY720(manufactured by Huntsman Advanced Materials LLC),” Araldite (registeredtrademark)” MY721 (manufactured by Huntsman Advanced Materials LLC.),“Araldite (registered trademark)” MY9512 (manufactured by HuntsmanAdvanced Materials LLC.),” Araldite (registered trademark)” MY9663(manufactured by Huntsman Advanced Materials LLC.), and “Epotohto(registered trademark)” YH-434 (manufactured by Tohto Kasei Co., Ltd.),and “jER (registered trademark)” 630 (manufactured by MitsubishiChemical Corporation).

Examples of commercially available products of the diaminodiphenylsulfone type epoxy resin include TG3DAS (manufactured by Mitsui FineChemicals, Inc.).

Examples of commercially available products of the aminophenol typeepoxy resin include ELM120 (manufactured by Sumitomo Chemical Co.,Ltd.), ELM100 (manufactured by Sumitomo Chemical Co., Ltd.), “jER(registered trademark)” 630 (manufactured by Mitsubishi ChemicalCorporation), “Araldite (registered trademark)” MY0500 (manufactured byHuntsman Advanced Materials LLC.), “Araldite (registered trademark)”MY0510 (manufactured by Huntsman Advanced Materials LLC.), “Araldite(registered trademark)” MY0600 (manufactured by Huntsman AdvancedMaterials LLC.), and “Araldite (registered trademark)” MY0610(manufactured by Huntsman Advanced Materials LLC.).

Examples of commercially available products of the bisphenol A typeepoxy resin include “EPON (registered trademark)” 825 (manufactured byMitsubishi Chemical Corporation), “EPICLON (registered trademark)” 850(manufactured by DIC Corporation), “Epotohto (registered trademark)”YD-128 (manufactured by Tohto Kasei Co., Ltd.), and DER-331 and DER-332(manufactured by The Dow Chemical Company).

Examples of commercially available products of the bisphenol F typeepoxy resin include “Araldite (registered trademark)” GY282(manufactured by Huntsman Advanced Materials LLC.), “jER (registeredtrademark)” 806, “jER (registered trademark)” 807, “jER (registeredtrademark)” 1750 (manufactured by Mitsubishi Chemical Corporation),“EPICLON (registered trademark)” 830 (manufactured by DIC Corporation),and “Epotohto (registered trademark)” YD-170 (manufactured by TohtoKasei Co., Ltd.).

In addition, in the epoxy resin composition of the present invention, anepoxy compound other than the above compound may be appropriatelycompounded.

The component [B] in the present invention is an aromatic diamine. Thepolyamine in which the aromatic diamine is included in the group has aplurality of amino groups capable of reacting with an epoxy group, andfunctions as a curing agent. Aromatic polyamines, particularly aromaticdiamines, are excellent as curing agents in that the cured epoxy resincan be provided with high mechanical properties and heat resistance.

Examples of those classified as aromatic diamines includediethyltoluenediamine such as 2,2′-diethyldiaminodiphenylmethane,2,4-diethyl-6-methyl-m-phenylenediamine,4,6-diethyl-2-methyl-m-phenylenediamine, and4,6-diethyl-m-phenylenediamine, 4,4′-methylenebis(N-methylaniline),4,4′-methylenebis(N-ethylaniline),4,4′-methylenebis(N-sec-butylaniline),N,N′-di-sec-butyl-p-phenylenediamine, 4,4′-diaminodiphenylmethane,3,3′-diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfone,3,3′-diisopropyl-4,4′-diaminodiphenylmethane,3,3′-di-t-butyl-4,4′-diaminodiphenylmethane,3,3′-diethyl-5,5′-dimethyl-4,4′-diaminodiphenylmethane,3,3′-di-t-butyl-5,5′-dimethyl-4,4′-diaminodiphenylmethane,3,3′,5,5′-tetraethyl-4,4′-diaminodiphenylmethane,3,3′-diisopropyl-5,5′-diethyl-4,4′-diaminodiphenylmethane,3,3′-di-t-butyl-5,5′-diethyl-4,4′-diaminodiphenylmethane,3,3′-di-t-butyl-5,5′-diisopropyl-4,4′-diaminodiphenylmethane, and3,3′,5,5′-tetra-t-butyl-4,4′-diaminodiphenylmethane. Of these,3,3′-diaminodiphenyl sulfone and 4,4′-diaminodiphenyl sulfone arepreferable, because the resulting cured product has excellent mechanicalproperties. In addition, a solid one is preferably used as the aromaticdiamine, and at least one of 3,3′-diaminodiphenyl sulfone and4,4′-diaminodiphenyl sulfone is particularly preferably included, fromthe viewpoint that an increase in viscosity when the epoxy resincomposition of the present invention is held at 70° C. can besuppressed, and consequently the pot life can be effectively improved.

Examples of commercially available products of the aromatic diamineinclude Seikacure-S(manufactured by Wakayama Seika Kogyo Co., Ltd.),MDA-220 (manufactured by Mitsui Chemicals, Inc.), “jER Cure (registeredtrademark)” WA (manufactured by Mitsubishi Chemical Corporation),3,3′-DAS (manufactured by Mitsui Chemicals, Inc.), “Lonzacure(registered trademark)” M-DEA (manufactured by Lonza Inc.), “Lonzacure(registered trademark)” M-DIPA (manufactured by Lonza Inc.), “Lonzacure(registered trademark)” M-MIPA (manufactured by Lonza Inc.), and“Lonzacure (registered trademark)” DETDA 80 (manufactured by LonzaInc.).

As the compounding amount of the aromatic diamine in the presentinvention, the ratio H/E between the amount by mole, E, of the epoxygroup of the component [A] to the amount by mole, H, of active hydrogenof the aromatic diamine is important to be 0.50 or more and 1.30 or less(condition (1)), preferably 0.70 or more and 1.20 or less, and morepreferably 0.80 or more and 1.10 or less. Setting H/E within such arange can appropriately form a cross-linked structure by the reactionbetween the epoxy resin and the aromatic diamine, and a cured resinhaving excellent strength and elongation can be obtained. In addition,setting H/E to 0.80 or more and 1.10 or less easily retains thecomponent [C] to be described later in the cross-linked structure, andthe effect of improving the elastic modulus, strength, and elongation isobtained.

In addition, in the epoxy resin composition of the present invention,the ratio between the amount by mole, E, of epoxy groups in thecomponent [A] and the total amount by mole for at least one of3,3′-diaminodiphenyl sulfone and 4,4′-diaminodiphenyl sulfone ((totalamount by mole for at least one of 3,3′-diaminodiphenyl sulfone and4,4′-diaminodiphenyl sulfone)/E) is preferably 0.50 or more and 1.30 orless. At 0.50 or more and 1.30 or less, more preferably 0.70 or more and1.20 or less, further preferably 0.80 or more and 1.10 or less, anincrease in viscosity when the epoxy resin composition of the presentinvention is held at 70° C. can be suppressed, and consequently, the potlife can be effectively improved.

The component [C] is a compound having a boiling point of 130° C. ormore, a molecular weight m of 50 or more and 250 or less, having noepoxy group in the molecule, and substantially having no curing abilityof an epoxy resin. Herein, compounds such as an amine and a phenol thatcan undergo an addition reaction with the epoxy resin, an acid anhydridethat can be copolymerized with the epoxy resin, imidazole that can be aself-polymerization reaction initiator of the epoxy resin, an aromaticurea compound, and a tertiary amine compound are compounds having thecuring ability of the epoxy resin, and do not correspond to compoundshaving no curing ability of the epoxy resin.

The component [C] is present in the void portion without beingincorporated into the cross-linked structure in the cross-linkedstructure formed by reaction of the epoxy resin and the aromaticdiamine, and the state thereof is maintained after curing. Thisincreases the elastic modulus of the resulting cured epoxy resin. Inaddition, the inventors surprisingly have found that not only a highelastic modulus but also a cured epoxy resin having high elongation andhigh strength can be obtained by compounding the component [C]. Thereason for this is not clear; however, the inventor considers asfollows. The component [C] has no epoxy group in the molecule andsubstantially has no curing ability of an epoxy resin, therebygenerating no reaction with the epoxy resin or the aromatic diamine thatforms a cross-linked structure. Therefore, the inventor considers thatthe component [C] is not bound by a covalent bond with a cross-linkedstructure formed by reaction of an epoxy resin and an aromatic diamine,and is appropriately held in the voids of the cross-linked structure,whereby voids in the cured product can be effectively filled, and theelastic modulus of the cured product is increased. In addition, theinventor considers that when distortion is imparted to the curedproduct, the component [C] can freely move in the cross-linkedstructure, and therefore the strain energy up to destruction can berelaxed, and the elongation and strength of the cured product areincreased.

The boiling point of the component [C] is 130° C. or more, morepreferably 180° C. or more, whereby volatilization of the component [C]when the epoxy resin composition is cured can be suppressed, and a curedresin or a fiber reinforced composite material excellent in mechanicalproperties can be obtained. Furthermore, generation of voids anddeterioration of mechanical properties in the obtained fiber reinforcedcomposite material can be suppressed. In the present invention, theboiling point is a value at normal pressure (101 kPa). In addition, whenthe boiling point at normal pressure cannot be measured, a convertedboiling point converted to 101 kPa in a boiling point conversion tablecan be used.

The molecular weight m of the component [C] is 50 or more and 250 orless, and more preferably 70 or more and 120 or less. Setting themolecular weight of the component [C] within such a range appropriatelyretains the component [C] in voids of a cross-linked structure formed byreaction of an epoxy resin and an aromatic diamine, and a cured productexcellent in elastic modulus, strength, and elongation is obtained.

The component [C] is preferably a compound having at least onefunctional group selected from the group consisting of an amide group, aketone group, and a hydroxyl group in the molecule. The component [C]has a highly polar functional group as described above in the molecule,whereby a strong intermolecular interaction acts between the hydroxylgroup in the cross-linked structure formed by the component [A] and thecomponent [B], and the component [C], and the component [C] is easilyand appropriately retained in the voids of the cross-linked structure,and therefore a particularly excellent effect of improving theelongation and strength is obtained.

The component [C] includes: amides such as N-methylformamide,N-methylacetamide, 2-pyrrolidone, N-methylpropionamide,N-ethylacetamide, N-methylacetanilide, and N,N′-diphenylacetamide; anddiols such as ethanediol, propanediol, butanediol, pentanediol,hexanediol, and heptanediol. These compounds may be used singly orappropriately used in combination.

The theoretical molecular weight between crosslinking points, M, of theepoxy resin composition of the present invention is preferably 500 orless, more preferably 400 or less, and still more preferably 250 orless. The theoretical molecular weight between crosslinking points, M,is preferably in such a range, because the component [C] is easilyretained in the voids of the cross-linked structure formed by thereaction between the epoxy resin and the aromatic diamine, and a curedproduct particularly excellent in elastic modulus, strength, andelongation is obtained.

Herein, the theoretical molecular weight between crosslinking points, M,is values derived by calculation from each component constituting theepoxy resin composition, and are values obtained by dividing the mass Wof all cured resins obtained by curing the epoxy resin composition bythe number N of crosslinking points of all cured resins. That is, it isconsidered that the void size in the cross-linked structure is larger asM is larger. Herein, the mass W of the all cured resins means the totalmass of all epoxy resin components and polyamine components included inthe epoxy resin composition, and the other components are not includedin the calculation.

The theoretical molecular weight between crosslinking points, M, isdetermined by the calculation described below. When k types (k is aninteger) of epoxy resin components are included in the epoxy resincomposition, the compounding amount of the i-th (i is an integer of 1 tok) epoxy resin component among them is a_(i) (unit: g). In addition,when the epoxy resin composition includes 1 types (1 is an integer) ofpolyamine components and the compounding amount of the j-th (j is aninteger of 1 to 1) polyamine among them is b_(j) (unit: g), the mass W(unit: g) of the all cured resins is obtained by formula (1).

[Mathematical Formula 1]

W=Σ _(i=1) ^(k) a _(i)+Σ_(j=1) ^(i) b _(j)  Formula (1)

The epoxy equivalent of the i-th epoxy resin component is E_(i), and thenumber of the epoxy group possessed by one molecule of the i-th epoxyresin component is x_(i). In addition, the active hydrogen equivalent ofthe j-th polyamine component is H_(j), and the number of the activehydrogen possessed by one molecule of the j-th polyamine component isy_(j). The number N of crosslinking points included in the all curedresins is determined differently depending on the case where thecompounding ratio between the epoxy resin and the polyamine isstoichiometric amount, the case where the polyamine is excessive, or thecase where the epoxy resin is excessive. The determination method to beadopted depends on a compounding ratio index β, which is obtained byformula (2), representing a compounding ratio between the epoxy resinand the polyamine.

[MathematicalFormula2] $\begin{matrix}{\beta = {\sum_{j = 1}^{l}{\frac{b_{j}}{H_{j}}/{\sum_{i = 1}^{k}\frac{a_{i}}{E_{i}}}}}} & {{Formula}(2)}\end{matrix}$

Herein, when β=1, the compounding ratio between the epoxy resin and thepolyamine is a stoichiometric amount, and the number N of crosslinkingpoints is obtained by formula (3). The number N of crosslinking pointsrepresents the number of crosslinking points generated by the reactionbetween all the reactive epoxy groups and the active hydrogen of all thepolyamines.

[MathematicalFormula3] $\begin{matrix}{N = {{\sum_{i = 1}^{k}\left\{ {\frac{a_{i}}{E_{i} \times x_{i}} \times \left( {x_{i} - 2} \right)} \right\}} + {\sum_{j = 1}^{l}\left\{ {\frac{b_{j}}{H_{j} \times y_{j}} \times \left( {y_{j} - 2} \right)} \right\}}}} & {{Formula}(3)}\end{matrix}$

In addition, when β>1, the polyamine is in excess of the stoichiometricamount, and the number N of crosslinking points is obtained by formula(4).

[MathematicalFormula4] $\begin{matrix}{N = {{\sum_{i = 1}^{k}\left\{ {\frac{a_{i}}{E_{i} \times x_{i}} \times \left( {x_{i} - 2} \right)} \right\}} + {\frac{1}{\beta} \times {\sum_{j = 1}^{l}\left\{ {\frac{b_{j}}{H_{j} \times y_{j}} \times \left( {y_{j} - 2} \right)} \right\}}}}} & {{Formula}(4)}\end{matrix}$

In addition, when β<1, the epoxy resin is in excess of thestoichiometric amount, and the number N of crosslinking points isobtained by formula (5).

[MathematicalFormula5] $\begin{matrix}{N = {{\beta \times {\sum_{i = 1}^{k}\left\{ {\frac{a_{i}}{E_{i} \times x_{i}} \times \left( {x_{i} - 2} \right)} \right\}}} + {\sum_{j = 1}^{l}\left\{ {\frac{b_{j}}{H_{j} \times y_{j}} \times \left( {y_{j} - 2} \right)} \right\}}}} & {{Formula}(5)}\end{matrix}$

Herein, E_(i)×x_(i) and H_(j)×y_(j) represent the average molecularweight of the i-th epoxy resin component and the average molecularweight of the j-th polyamine component, respectively. In addition,(x_(i)−2) represents the number of crosslinking points generated whenall the epoxy groups in one molecule of the i-th epoxy resin componentreact with the active hydrogen of the polyamine and are incorporatedinto the cross-linked structure. In addition, (y_(j)−2) represents thenumber of crosslinking points generated when all the active hydrogens inone molecule of the j-th polyamine react with the epoxy group and areincorporated into the cross-linked structure. For example, when the i-thepoxy resin component is a tetrafunctional epoxy resin, one molecule hasfour epoxy groups, and the number of crosslinking points generated is4-2, that is 2. In the case of a monofunctional epoxy resin, the numberof crosslinking points generated is calculated as 0. In addition, whenthe j-th polyamine component has two active hydrogens per molecule, thenumber of crosslinking points generated is 2-2, that is, 0. Thetheoretical molecular weight between crosslinking points, M, isdetermined by formula (6), using W and N determined by the aboveformula.

[MathematicalFormula6] $\begin{matrix}{M = \frac{W}{N}} & {{Formula}(6)}\end{matrix}$

Herein, as an example, the theoretical molecular weight betweencrosslinking points, M, is determined for the cured resin of the epoxyresin composition composed of 90 g of an epoxy resin 1 (number of epoxygroups: 3, epoxy equivalent: 98 g/eq), 10 g of an epoxy resin 2 (numberof epoxy groups: 2, epoxy equivalent: 135 g/eq), and 44.7 g of apolyamine 1 (number of active hydrogen: 4, active hydrogen equivalent:45 g/eq). The mass W of the all cured resins is 144.7 g according to theformula (1). In addition, β obtained by the formula (2) is 1, andtherefore the number N of crosslinking points of the all cured resins isobtained as 0.803 by the formula (3). Therefore, the theoreticalmolecular weight between crosslinking points, M, of the cured resin isdetermined to be 180 by the formula (6).

In the epoxy resin composition of the present invention, it is alsoimportant that at least a part of the component [C] satisfies 0.10 ormore and 0.60 or less in a ratio m/M of a molecular weight m thereof toa theoretical molecular weight between crosslinking points, M, of acured product of the epoxy resin composition (condition (2)). In thepresent invention, the elastic modulus, strength, and elongation of thecured resin are improved by compounding the component [C] having anappropriate molecular weight with respect to the void size of thecross-linked structure formed by the reaction between the epoxy resinand the aromatic diamine. However, the void size of the cross-linkedstructure formed by the reaction between the epoxy resin and thearomatic diamine varies one by one depending on the type of epoxy resinor aromatic diamine used. Therefore, setting m/M within the above rangeappropriately retains the component [C] in the voids of the cross-linkedstructure, and a cured product excellent in elastic modulus, strength,and elongation is obtained. Preferably setting m/M to 0.30 or more and0.50 or less provides a cured product having particularly excellentelastic modulus, strength, and elongation.

In the epoxy resin composition of the present invention, it is importantthat the ratio C/E of the amount by mole, E, of epoxy groups of thecomponent [A] to the amount by mole, C, of the component [C] satisfyingthe condition (2) is 0.01 or more and 0.20 or less (condition (3)).Setting C/E within such a range appropriately retains the component [C]in voids of a cross-linked structure formed by reaction of an epoxyresin and an aromatic diamine, and a cured product excellent in elasticmodulus, strength, and elongation is obtained. In addition, setting them/M to 0.30 or more and 0.50 or less and further setting C/E topreferably 0.07 or more and 0.20 or less provide a cured product havinga particularly high elastic modulus. In addition, setting the m/M to0.30 or more and 0.50 or less and further setting C/E to preferably 0.01or more and 0.13 or less provide a cured product having a particularlyhigh strength. Furthermore, setting the m/M to 0.30 or more and 0.50 orless and further setting C/E to preferably 0.07 or more and 0.13 or lessprovides a cured product having particularly excellent both elasticmodulus and strength.

It is also important that the viscosity of the resin composition of thepresent invention when held at 70° C. for 2 hours is 5.0 times or lessthe initial viscosity at 70° C. (condition (4)). Setting the ratio (alsoreferred to as “viscosity increase ratio”) to 5.0 times or less, morepreferably 3.0 times or less, and still more preferably 2.5 times orless reduces the viscosity change of the resin composition in the stepof kneading the resin composition or the step of impregnatingreinforcing fibers with the resin composition, allowing prolonging thepot life. In addition, variations in the flow amount of the resincomposition during molding can be reduced, and variations in the contentof the resin included in the fiber reinforced composite material can besuppressed, thereby allowing providing a fiber reinforced compositematerial having stable dimensions and mechanical characteristics.

The viscosity increase ratio can be effectively suppressed by using asolid aromatic diamine of the component [B], particularly at least oneof 3,3′-diaminodiphenyl sulfone and 4,4′-diaminodiphenyl sulfone.

The epoxy resin composition of the present invention is excellent inelastic modulus, strength, and elongation, and is preferably used as amatrix resin of a fiber reinforced composite material. That is, thefiber reinforced composite material of the present invention includes acured product of the epoxy resin composition of the present inventionand a reinforcing fiber.

Examples of a method for obtaining a fiber reinforced composite materialinclude a method in which a reinforcing fiber is impregnated with aresin composition in a molding step, such as a hand lay-up method, anRTM method, a filament winding method, and a pultrusion method, and amethod of molding a prepreg in which a reinforcing fiber is previouslyimpregnated with a resin composition by an autoclave method or a pressmolding method. Of these, the arrangement of the fibers and the ratio ofthe resin can be precisely controlled and the properties of thecomposite material can be maximized, and therefore it is preferable topreviously prepare a prepreg including an epoxy resin composition and areinforcing fiber. That is, the prepreg of the present inventionincludes the epoxy resin composition according to the present inventionand a reinforcing fiber.

Preferable examples of the reinforcing fiber used in the prepreg of thepresent invention and the fiber reinforced composite material of thepresent invention include carbon fiber, graphite fiber, aramid fiber,and glass fiber, and the carbon fiber is particularly preferable. Theform and arrangement of the reinforcing fiber are not limited, and forexample, fibrous structures such as a long fiber aligned in onedirection, a single tow, woven fabric, knitting, and a braid are used.Two or more types of carbon fibers, glass fibers, aramid fibers, boronfibers, PBO fibers, high-strength polyethylene fibers, alumina fibers,and silicon carbide fibers may be used in combination as the reinforcingfiber.

Specific examples of the carbon fiber include acrylic-based,pitch-based, and rayon-based carbon fibers, and particularly, theacrylic-based carbon fiber having high tensile strength is preferablyused.

Twisted yarns, untwisted yarns, and non-twisted yarns can be used as theform of the carbon fibers, and in the case of twisted yarns, theorientation of the filament constituting the carbon fiber is notparallel, thus causing a decrease in mechanical properties of theresulting carbon fiber reinforced composite material, and thereforethere are preferably used untwisted yarns or non-twisted yarns having agood balance between moldability and strength properties of the carbonfiber reinforced composite material.

The carbon fiber preferably has a tensile elastic modulus of 200 GPa ormore and 440 GPa or less. The tensile elastic modulus of the carbonfiber is affected by the crystallinity of the graphite structureconstituting the carbon fiber, and the elastic modulus is improved asthe crystallinity is higher. This range is preferable, because all ofrigidity and strength of the carbon fiber reinforced composite materialare balanced at a high level. The elastic modulus is more preferably 230GPa or more and 400 GPa or less, still more preferably 260 GPa or moreand 370 GPa or less. Herein, the tensile elastic modulus of the carbonfiber is a value measured according to JIS R7608 (2008).

The prepreg of the present invention can be produced by various knownmethods. For example, a prepreg can be produced by a hot melt method inwhich a resin composition is heated to reduce the viscosity withoutusing an organic solvent, and a reinforcing fiber is impregnatedtherewith.

In addition, for the hot melt method, there can be used, for example, amethod of directly impregnating a reinforcing fiber with a resincomposition whose viscosity has been reduced by heating, or a method offirst preparing a release paper sheet with a resin film in which therelease paper is once coated with the resin composition, thensuperimposing the resin film on the reinforcing fiber side from bothsides or one side of the reinforcing fiber, and heating and pressurizingto impregnate the reinforcing fiber with the resin composition.

The content of a reinforcing fiber in a prepreg is preferably 30% bymass or more and 90% by mass or less. At 30% by mass or more, morepreferably 35% by mass or more, and still more preferably 65% by mass ormore, it is easy to obtain an advantage of a fiber reinforced compositematerial excellent in specific strength and specific modulus. Inaddition, it is possible to prevent the amount of heat generation duringcuring from becoming too high during molding of the fiber reinforcedcomposite material. Whereas, at 90% by mass or less, more preferably 85%by mass or less, generation of voids in the composite material due topoor impregnation of the resin can be suppressed. In addition, thetacking property of a prepreg can be maintained.

The fiber reinforced composite material of the present invention can beproduced by a method in which the above-described prepreg of the presentinvention is laminated in a predetermined form and pressurized andheated to cure the resin as an example. Herein, for example, a pressmolding method, an autoclave molding method, a bagging molding method, awrapping method, and an internal pressure molding method are adopted asa method of providing heat and pressure.

The fiber reinforced composite material of the present invention can bewidely used in aerospace applications, general industrial applications,and sports applications. More specifically, preferable examples ofgeneral industrial applications include structures such as automobiles,ships, and railway vehicles. Preferable examples of sports applicationsinclude applications such as golf shafts, fishing rods, and rackets oftennis and badminton.

EXAMPLES

Hereinafter, the present invention will be described in more detail withreference to Examples. However, the scope of the present invention isnot limited only to these examples. The unit “part” of the compositionratio refers to part by mass unless otherwise noted. In addition,measurement of various properties (physical properties) was performedunder the environment of a temperature of 23° C. and a relative humidityof 50% unless otherwise noted.

<Materials Used in Examples and Comparative Examples>

(1) Component [A]: epoxy resin

-   -   “Araldite (registered trademark)” MY0600 (aminophenol type epoxy        resin, epoxy equivalent: 118 g/eq, number of epoxy groups: 3,        manufactured by Huntsman Advanced Materials LLC)    -   “jER (registered trademark)” 825 (bisphenol A epoxy resin, epoxy        equivalent: 170 g/eq, number of epoxy groups: 2, manufactured by        Mitsubishi Chemical Corporation)    -   Glycidol (molecular weight: 74, epoxy equivalent: 74 g/eq,        number of epoxy groups: 1, boiling point: 167° C., manufactured        by Tokyo Chemical Industry Co., Ltd.)

(2) Component [B]: aromatic diamine

-   -   3,3′-DAS (3,3′-diaminodiphenylsulfone, active hydrogen        equivalent: 62 g/eq, number of active hydrogens: 4, manufactured        by Mitsui Fine Chemicals, Inc.)    -   Seikacure-S(4,4′-diaminodiphenylsulfone, active hydrogen        equivalent: 62 g/eq, number of active hydrogens: 4, manufactured        by Wakayama Seika Kogyo Co., Ltd.)    -   “jER Cure (registered trademark)” WA (diethyltoluenediamine,        active hydrogen equivalent: 45 g/eq, number of active hydrogens:        4, manufactured by Mitsubishi Chemical Corporation)

(3) Component [C]: a compound having a boiling point of 130° C. or moreand a molecular weight m of 50 to 250, the compound having no epoxygroup in the molecule and having substantially no curing ability of anepoxy resin

-   -   1,2-ethanediol (boiling point: 197° C., molecular weight m: 62,        manufactured by Tokyo Chemical Industry Co., Ltd.)    -   1,2-propanediol (boiling point: 188° C., molecular weight m: 76,        manufactured by Tokyo Chemical Industry Co., Ltd.)    -   1,2-hexanediol (boiling point: 245° C., molecular weight m: 118,        manufactured by Tokyo Chemical Industry Co., Ltd.)    -   N-methylpropionamide (boiling point: 223° C., molecular weight        m: 87, manufactured by Tokyo Chemical Industry Co., Ltd.)    -   N,N′-diphenylacetamide (boiling point (converted value): 410°        C., molecular weight m: 211, manufactured by Tokyo Chemical        Industry Co., Ltd.)    -   1,2-octanediol (boiling point: 267° C., molecular weight m: 146,        manufactured by Tokyo Chemical Industry Co., Ltd.)

(4) Other Compounds

-   -   ethanol (boiling point: 78° C., molecular weight m: 46,        manufactured by Tokyo Chemical Industry Co., Ltd.)    -   N,N′-diphenyl-4-methoxybenzamide (boiling point: 468° C.,        molecular weight m: 303, manufactured by Tokyo Chemical Industry        Co., Ltd.)

<Various Evaluation Methods>

The epoxy resin composition of each example was measured by using thefollowing measurement methods.

(1) Three-Point Bending Measurement of Cured Resin

The uncured resin composition was defoamed in a vacuum, then heated at arate of 1.7° C./min from 30° C. in a mold set to have a thickness of 2mm with a 2 mm thick “Teflon (registered trademark)” spacer, held at atemperature of 125° C. for 5 hours, then heated at a rate of 1.7°C./min, and cured at a temperature of 225° C. for 2 hours to provide aplate-shaped cured resin having a thickness of 2 mm. A test piece havinga width of 10 mm and a length of 60 mm was cut out from the cured resin,and an Instron universal testing machine (manufactured by Instron Inc.)was used to set the span to 32 mm, the crosshead speed to 2.5 mm/min,and the number of samples to n=6, and to perform three-point bendingaccording to JIS K7171 (1994), and the average values of the elasticmodulus, the strength, and the elongation were defined as the elasticmodulus, the strength, and the elongation of the cured resin,respectively.

(2) Measurement of Viscosity of Resin Composition

Using a dynamic viscoelasticity measuring apparatus ARES-G2(manufactured by TA Instruments Inc.), an epoxy resin composition wasset so that the distance between the upper and lower jigs was 1 mm byusing flat parallel plates having a diameter of 40 mm as the upper andlower measuring jigs, and the initial viscosity of the epoxy resincomposition at 70° C. in a torsion mode (measurement frequency: 0.5 Hz)and the viscosity in holding at 70° C. for 2 hours in a state of settingin the apparatus were each measured. In addition, the viscosity inholding at 70° C. for 2 hours was divided by the initial viscosity at70° C. to provide a viscosity increase ratio.

Example 1

(Production of Resin Composition)

A resin composition was prepared by the following method.

100 parts of “Araldite (registered trademark)” MY0600 as the component[A] described in Table 1 was charged into a kneading apparatus, heatedto a target temperature of 55 to 65° C. while being kneaded, 53 parts of3,3′-DAS as the component [B] was added, and stirring was performed for30 minutes. Thereafter, 5 parts of 1,2-ethanediol was added as thecomponent [C], and stirring was further performed for 10 minutes toprovide a resin composition.

In this case, the ratio H/E between the amount by mole, H, of activehydrogen of the component [B] and the amount by mole, E, of the epoxygroup of the component [A] was 1.00. In addition, the ratio C/E of theamount by mole, C, of the component [C] to the amount by mole, E, of theepoxy group of the component [A] was 0.10. In addition, the theoreticalmolecular weight between crosslinking points, M, of the epoxy resincomposition composed of the component [A] and component [B] was 216, themolecular weight m of the component [C] was 62, and m/M was 0.29.

As a result of three-point bending measurement of the cured resin of theobtained resin composition, the elastic modulus was 5.1 GPa, thestrength was 225 MPa, and the elongation was 5.9%. As compared withComparative Example 1 (without compounding of the component [C])described later, excellent elastic modulus, strength, and elongationwere obtained. In addition, the viscosity in holding at 70° C. for 2hours was 2.2 times the initial viscosity at 70° C., providing asufficient pot life.

Examples 2 to 12

The components [A], [B] and [C] were compounded according to thecompounding ratios in Tables 1 and 2 in the same procedure as in Example1 to provide resin compositions.

The various measurement results of Examples are as shown in Tables 1 and2, and excellent elastic modulus, strength, and elongation of the curedresin were obtained when the compounding of the resin composition waschanged as in Examples 2 to 12. In addition, the viscosity increaseratio was good.

Comparative Examples 1 to 10

The components [A] and [B] (and [C] or a substitute thereof) werecompounded according to the compounding ratio in Table 2 in the sameprocedure as in Example 1 to provide resin compositions.

In Comparative Example 1, those corresponding to the component [C] wasnot compounded. When Comparative Example 1 is compared with Example 1,it is found that the elastic modulus, strength, and elongation of thecured resin are each improved by compounding the component [C], andparticularly the strength and elongation are dramatically improved.

In Comparative Example 2, those corresponding to the component [C] wasalso not compounded. Comparison of Comparative Example 2 with Example 6shows that compounding the component [C] dramatically improves theelastic modulus and strength of the cured resin.

In Comparative Example 3, ethanol was compounded instead of thecomponent [C]. Ethanol does not satisfy the condition that the boilingpoint of the component [C] is 130° C. or more and the condition that themolecular weight m is 50 or more and 250 or less. Comparison betweenComparative Example 3 and Example 1 shows that the elastic modulus,strength, and elongation of the resulting cured resin are improved bycompounding the component [C] satisfying the requirements that theboiling point is 130° C. or more and the molecular weight m is 50 ormore and 250 or less.

In Comparative Example 4, N,N′-diphenyl-4-methoxybenzamide wascompounded instead of the component [C].N,N′-diphenyl-4-methoxybenzamide does not satisfy the condition that themolecular weight m in the component [C] is 50 or more and 250 or less.In addition, there is not satisfied the condition that the ratio m/Mbetween the theoretical molecular weight between crosslinking points, M,of the epoxy resin composition and the molecular weight m of thecomponent [C] is 0.10 or more and 0.60 or less. Comparison betweenComparative Example 4 and Example 1 shows that satisfying the aboveconditions improves the elastic modulus, strength, and elongation of theresulting cured resin.

In Comparative Example 5, glycidol was compounded instead of thecomponent [C]. Glycidol has an epoxy group in the molecule. Comparisonbetween Comparative Example 5 and Example 1 shows that the component [C]having no epoxy group in the molecule improves the elastic modulus,strength, and elongation of the resulting cured resin.

Comparative Examples 6 and 7 does not satisfy the condition that theratio H/E between the amount by mole, E, of the epoxy group of thecomponent [A] and the amount by mole, H, of active hydrogen of thecomponent [B] is 0.50 or more and 1.30 or less. Comparison betweenComparative Examples 6 and 7 and Example 1 shows that satisfying theabove conditions improves the strength of the resulting cured resin.

Comparative Example 8 does not satisfy the condition that the ratio C/Ebetween the amount by mole, E, of the epoxy group of the component [A]and the amount by mole, C, of the epoxy group of the component [C] is0.01 or more and 0.20 or less. Comparison between Comparative Example 8and Example 1 shows that satisfying the above conditions improves theelastic modulus, strength, and elongation of the resulting cured resin.

Comparative Example 9 does not satisfy the condition that the ratio m/Mbetween the theoretical molecular weight between crosslinking points, M,of the epoxy resin composition including the components [A] and [B] andthe molecular weight m of the component [C] is 0.10 or more and 0.60 orless. Comparison between Comparative Example 9 and Example 1 shows thatsatisfying the above conditions improves the elastic modulus, strength,and elongation of the resulting cured resin.

Comparative Example 10 does not satisfy the condition that the viscosityof the epoxy resin composition held at 70° C. for 2 hours is 5.0 timesor less the initial viscosity at 70° C. Therefore, the composition had alarge increase in viscosity in the step of mixing the epoxy resin and ashort pot life. Comparison between Comparative Example 10 and Example 1shows that satisfying the above conditions provides a long pot life ofthe resulting resin composition and thus excellent handleability.

Herein, comparing Example 2, Example 5, Example 6, Example 7,Comparative Example 1, and Comparative Example 8, these are epoxy resincompositions including the same component [A], component [B], andcomponent [C], and differ only in the compounding amount of thecomponent [C]. FIG. 1 shows the relationship between the ratio C/E ofthe amount by mole, C, of the component [C] to the amount by mole, E, ofthe epoxy group of the component [A] and the elastic modulus, and FIG. 2shows the relationship with the strength. From FIGS. 1 and 2 , it isfound that C/E is 0.01 or more and 0.20 or less in the epoxy resincomposition of the present invention, thereby providing a cured productexcellent in elastic modulus, strength, and elongation. In addition, itis found that C/E is 0.07 or more and 0.20 or less, thereby providing acured product particularly excellent in elastic modulus, and C/E is 0.01or more and 0.13 or less, thereby providing a cured product particularlyexcellent in strength.

Furthermore, Example 1, Example 2, Example 3, Example 4, ComparativeExample 1, and Comparative Example 9 are epoxy resin compositionsincluding the same component [A] and component [B] at the samecompounding ratio, and the type of the component [C] is different or notused. The relationship between m/M and the elastic modulus is shown inFIG. 3 , and the relationship with the strength is shown in FIG. 4 .Comparison of Example 1, Example 2, Example 3, Example 4, ComparativeExample 1, and Comparative Example 9 in FIGS. 3 and 4 shows that therelationship of 0.10 m/M 0.60 is satisfied in the resin composition ofthe present invention, thereby providing a cured product excellent inthe elastic modulus and strength of the cured resin. In addition, whenthe relationship of 0.30<m/M<0.50 is satisfied, it is found that a curedproduct particularly excellent in elastic modulus, strength, andelongation is obtained.

TABLE 1 Example Example Example Example Example Example 1 2 3 4 5 6Component ″Araldite (registered 100 100 100 100 100 100 [A] trademark)″MY0600 ″jER″ ® 825 — — — — — — Glycidol — — — — — — Component 3,3′-DAS53 53 53 53 53 53 [B] SEIKACURE S — — — — — — ″jER Cure″ (registered — —— — — — trademark) WA Component 1,2-Ethanediol 5 — — — — — [C]1,2-Propanediol — 7 — — 1 3 1,2-Hexanediol — — 10 — — —N-methylpropionamide — — — 7 — — N,N′-diphenylacetamide — — — — — —1,2-Octanediol — — — — — — Other Ethanol — — — — — — compound [C′]N,N′-diphenyl-4- — — — — — — methoxybenzamide Properties H/E 1.00 1.001.00 1.00 1.00 1.00 of resin Boiling point of [C] 197 188 245 220 188188 composition or [C′] (° C.) Molecular weight m of 62 76 118 87 76 76[C] or [C′] Theoretical molecular 216 216 216 216 216 216 weight betweencrosslinking points, M m/M 0.29 0.35 0.55 0.40 0.35 0.35 C/E 0.10 0.100.10 0.10 0.02 0.05 Initial viscosity at 70° C. 0.8 0.5 0.4 0.5 0.9 0.8(Pa·s) Viscosity in holding at 1.8 1.1 0.9 0.8 1.4 1.4 70° C. for 2hours (Pa·s) Viscosity increase ratio 2.2 2.2 2.2 1.5 1.6 1.7 in holdingat 70° C. for 2 hours (times) Properties Elastic modulus (GPa) 5.1 5.35.1 5.4 5.0 5.1 of cured Strength (MPa) 225 225 201 240 222 222 resinElongation (%) 5.9 5.5 4.8 6.3 5.6 5.8 Example Example Example ExampleExample 7 8 9 10 11 Component ″Araldite (registered 100 100 100 — — [A]trademark)″ MY0600 ″jER″ ® 825 — — — 100 100 Glycidol — — — — —Component 3,3′-DAS 53 32 63 35 29 [B] SEIKACURE S — — — — — ″jER Cure″(registered — — — — — trademark) WA Component 1,2-Ethanediol — 5 5 — —[C] 1,2-Propanediol 10 — — 4 4 1,2-Hexanediol — — — — —N-methylpropionamide — — — — — N,N′-diphenylacetamide — — — — —1,2-Octanediol — — — — — Other Ethanol — — — — — compound [C′]N,N′-diphenyl-4- — — — — — methoxybenzamide Properties H/E 1.00 0.601.20 1.00 0.80 of resin Boiling point of [C] 188 197 197 188 188composition or [C′] (° C.) Molecular weight m of 76 62 62 76 76 [C] or[C′] Theoretical molecular 216 310 231 464 554 weight betweencrosslinking points, M m/M 0.35 0.20 0.27 0.16 0.14 C/E 0.16 0.10 0.100.10 0.10 Initial viscosity at 70° C. 0.4 0.5 1.2 0.4 0.3 (Pa·s)Viscosity in holding at 0.8 1.0 2.9 0.6 0.5 70° C. for 2 hours (Pa·s)Viscosity increase ratio 2.1 2.0 2.4 1.6 1.6 in holding at 70° C. for 2hours (times) Properties Elastic modulus (GPa) 5.2 5.3 5.0 3.8 3.6 ofcured Strength (MPa) 180 216 220 170 161 resin Elongation (%) 3.9 4.85.8 10 or 10 or more more

TABLE 2 Example Comparative Comparative Comparative ComparativeComparative 12 Example 1 Example 2 Example 3 Example 4 Example 5Component ″Araldite (registered — 100 — 100 100 100 [A] trademark)″MY0600 ″jER″ ® 825 100 — 100 — — — Glycidol — — — — — 6 Component3,3′-DAS 35 53 35 53 53 58 [B] SEIKACURE S — — — — — — ″jER Cure″(registered — — — — — — trademark) WA Component 1,2-Ethanediol — — — — —— [C] 1,2-Propanediol — — — — — — 1,2-Hexanediol — — — — — —N-methylpropionamide — — — — — — N,N′-diphenylacetamide 12 — — — — —1,2-Octanediol — — — — — — Other Ethanol — — — 4 — — compoundN,N′-diphenyl-4- — — — — 17 — [C′] methoxybenzamide Properties H/E 1.001.00 1.00 1.00 1.00 1.00 of resin Boiling point of [C] 410 — — 78 468 —composition or [C′] (° C.) Molecular weight m of 211 — — 46 303 — [C] or[C′] Theoretical molecular 464 216 474 216 216 246 weight betweencrosslinking points, M m/M 0.45 — — 0.21 1.40 — C/E 0.10 0.00 0.00 0.000.00 0.00 Initial viscosity at 70° C. 0.2 1.0 0.5 0.8 0.3 0.6 (Pa·s)Viscosity in holding at 0.3 1.7 1.2 1.7 0.5 1.4 70° C. for 2 hours(Pa·s) Viscosity increase ratio 1.7 1.6 2.7 2.1 1.7 2.4 in holding at70° C. for 2 hours (times) Properties Elastic modulus (GPa) 3.9 5.0 3.45.0 4.9 5.0 of cured Strength (MPa) 171 181 152 180 172 188 resinElongation (%) 8.2 4.2 10 or more 4.2 4.3 4.4 Comparative ComparativeComparative Comparative Comparative Example 6 Example 7 Example 8Example 9 Example 10 Component ″Araldite (registered 100 100 100 100 100[A] trademark)″ MY0600 ″jER″ ® 825 — — — — — Glycidol — — — — —Component 3,3′-DAS 24 74 53 53 6 [B] SEIKACURE S — — — — 6 ″jER Cure″(registered — — — — 29 trademark) WA Component 1,2-Ethanediol 5 5 — — —[C] 1,2-Propanediol — — 15 — 1 1,2-Hexanediol — — — — —N-methylpropionamide — — — — — N,N′-diphenylacetamide — — — — —1,2-Octanediol — — — 13 — Other Ethanol — — — — — compoundN,N′-diphenyl-4- — — — — — [C′] methoxybenzamide Properties H/E 0.451.40 1.00 1.00 0.84 of resin Boiling point of [C] 197 197 188 267 188composition or [C′] (° C.) Molecular weight m of 62 62 76 146 76 [C] or[C′] Theoretical molecular 389 246 216 216 215 weight betweencrosslinking points, M m/M 0.16 0.25 0.35 0.68 0.35 C/E 0.10 0.10 0.230.00 0.02 Initial viscosity at 70° C. 0.3 1.6 0.2 0.2 0.2 (Pa·s)Viscosity in holding at 0.6 4.5 0.4 0.5 1.4 70° C. for 2 hours (Pa·s)Viscosity increase ratio 1.8 2.8 2.2 2.3 7.5 in holding at 70° C. for 2hours (times) Properties Elastic modulus (GPa) 5.4 4.9 5.0 4.9 — ofcured Strength (MPa) 161 184 161 193 — resin Elongation (%) 3.9 6.2 3.64.7 —

1-5. (canceled)
 6. An epoxy resin composition comprising the followingcomponents [A] to [C]: [A]: epoxy resin; [B]: aromatic diamine; and [C]:a compound having a boiling point of 130° C. or more and a molecularweight m of 50 or more and 250 or less, the compound having no epoxygroup in a molecule and having substantially no curing ability of anepoxy resin, and satisfying the following conditions (1) to (5): (1) aratio H/E between an amount by mole, E, of an epoxy group in thecomponent [A] and an amount by mole, H, of active hydrogen in thecomponent [B] is 0.50 or more and 1.30 or less; (2) at least a part ofthe component [C] satisfies 0.10 or more and 0.60 or less in a ratio m/Mbetween a molecular weight m thereof and a theoretical molecular weightbetween crosslinking points, M, of a cured product of an epoxy resincomposition; (3) a ratio C/E between an amount by mole, E, of an epoxygroup of the component [A] and an amount by mole, C, of the component[C] satisfying the condition (2) is 0.01 or more and 0.20 or less; (4)viscosity at 70° C. for 2 hours is 5.0 times or less initial viscosityat 70° C.; and (5) a theoretical molecular weight between crosslinkingpoints, M, of a cured product of the epoxy resin composition is 500 orless.
 7. The epoxy resin composition according to claim 6, wherein thecomponent [C] is a compound having at least one functional groupselected from the group consisting of an amide group, a ketone group,and a hydroxyl group in a molecule.
 8. A prepreg comprising the epoxyresin composition according to claim 6 and a reinforcing fiber.
 9. Afiber reinforced composite material comprising a cured product of theepoxy resin composition according to claim 6 and a reinforcing fiber.